1. FIELD OF THE INVENTION
This invention relates to a starting motor with an intermediate gear utilized in a vehicle, particularly to sealing of a bearing of an intermediate gear thereof.
2. DISCUSSION OF BACKGROUND
FIG. 3 is a longitudinal sectional diagram showing a conventional starting motor with an intermediate gear. A reference numeral 1 designates a DC motor, wherein a rotating shaft 3 is extended from an armature 2 and a field pole 6 is attached to a yoke 5 of a stator 4. A numeral 7 designates a front bracket connected to the yoke 5, which supports a front end of the rotating shaft 3 through a bearing 8.
A numeral 10 designates an overrunning clutch supported by the rotating shaft 3 slidably in the axial direction, composed as follows. A numeral 11 designates a clutch outer connected to a periphery of the rotating shaft 3 by a helical spline 9 thereby transmitting the rotation, and 12, a clutch inner to which a one-way rotation is transmitted through rollers 13 from the clutch outer 11, which is supported by the rotating shaft 3 through a sleeve bearing 19. A pinion 14 is integrally formed at a front end of the clutch inner 12. A numeral 15 designates a clutch cover fixed to the clutch outer 11 by calking through a holding plate 16, and 17, a stop ring attached to the clutch outer 11. An engaging groove 18 is formed between the stop ring and a stepped portion of the clutch outer. A numeral 20 designates a stopper attached to the rotating shaft which restrains a forward movement position of the overrunning clutch 10.
A numeral 21 designates a shift lever, an intermediate fulcrum of which is supported by the front bracket 7 and a receiving body 24 that is received by a grommet 22 attached to the yoke 5, through a compression spring 23, and a forked lower end of which engages with the engaging grooves 18 in the axial direction. An upper end of the shift lever 21 engages with a front end of a plunger of an electromagnetic switch (not shown) of the motor 1 in the axial direction and the shift lever 21 swivels around the fulcrum.
A numeral 25 designates an intermediate shaft fixed to the front bracket 7 in parallel with the rotating shaft 3, 26, a grommet inserted into a hole of the intermediate shaft of the front bracket 7, and 27, an intermediate gear supported by the intermediate shaft 25 rotatably and slidably in the axial direction, through a sleeve bearing 28 which is fixed to an inner periphery thereof, which meshes with a pinion 14. The sleeve bearing 28 is made of a non-oil-feeding sintering alloy. A numeral 29 designates a ring-like co-rotating body fixed to an outer periphery of the clutch cover 15, of which flange 29a engages with an engaging groove 27a at an outer periphery of a boss of the intermediate gear 27. The intermediate gear 27 moves forwardly and backwardly in accordance with a forward and a backward movement of the overrunning clutch 10, through the ring-like co-rotating body 29. A numeral 30 designates a ring-gear provided at a flywheel of an internal combustion engine, which meshes with the intermediate gear 27 by the forward movement thereof, thereby starting to rotate the internal combustion engine.
Next, explanation will be given to the operation. When current flows in an excitation coil of the electromagnetic switch, the plunger is drawn and swivels the shift lever 21 in the counterclockwise direction in FIG. 3. By this operation, the overrunning clutch 10 moves forwardly and is received by the stopper 20. By the forward movement of the overrunning clutch 10, the intermediate gear 27 moves forwardly by the ring-like co-rotational body 29 and meshes with the ring gear 30. Next, fixed terminals of the electromagnetic switch are closed, current flows in a circuit of the DC motor 1, the armature 2 starts rotating, the rotation of the rotating shaft 3 is transmitted to the intermediate gear 27 through the overrunning clutch 10 and the pinion 14 and the rotation is transmitted to the ring-gear 30, thereby starting up the internal combustion engine.
In the above conventional starting motor with an intermediate gear, by meshing the pinion 14 with the ring-gear 30, the sleeve bearing 28 of the intermediate gear 27 is applied with a force approximately twice as much as that in meshing a pair of gears. The sleeve bearing 28 is composed of a sintered alloy and the mechanical strength thereof is weak compared with a general bearing. Therefore, the service life thereof is shortened. Especially, in case of a means of transmitting the rotation of the armature 2 to the overrunning clutch through a planetary gear speed reducing device, the torque thereof is increased thereby further decreasing the service life of the sleep bearing 28. Furthermore, the front bracket 7 is provided with a large opening owing to the intermediate gear 27. Therefore, outside dusts are attached to the intermediate shaft 25, which invade into a bearing surface of the sleeve bearing 28 thereby damaging the bearing surface.